## Why
Sparse and out-of-order rate-limit updates can omit account metadata or let an
older full read overwrite a newer workspace hard stop. Credit availability also
does not always include a displayable balance.
## What changed
- Propagate the backend's `spendControlReached` state through rate-limit
snapshots and the app-server protocol, preserving it across sparse updates.
- Keep workspace hard-stop classifications for error routing and ignore stale
full-read results after a newer hard-stop notification.
- Base TUI warnings and model-switch prompts on credit availability and hard-stop
state, and show `Credits: Available` when a finite balance is hidden.
## Testing
Added coverage for spend-control mapping, snapshot merging, out-of-order reads,
workspace error routing, warning and prompt behavior, and credit status display.
GitOrigin-RevId: 18b09d493d5a620a7c079fb721ec50b38dd5b04c